Various strains belonging to the genus Corynebacterium or Brevibacterium and being capable of producing L-tryptophan have been constructed by recombinant DNA technology. They include strains carrying a recombinant DNA that contains a gene coding for anthranilate synthase (hereinafter abbreviated to AS) [Japanese Published Unexamined Patent Application No. 156292/1984 (European Publication No. 136359)], strains carrying a recombinant DNA that contains genes coding for anthranilate phosphoribosyl transferase (hereinafter abbreviated to PRT), N-5'-phosphoribosyl anthranilate isomerase (hereinafter abbreviated to PRAI), indole-3-glycerol phosphate synthase (hereinafter abbreviated to InGPS) and tryptophan synthase (hereinafter abbreviated to TS) (Japanese Published Unexamined Patent Application No. 149082/1986), strains carrying a recombinant DNA that contains a gene coding for 3-deoxy-D-arabino-hepturosonate-7-phosphate synthase (hereinafter abbreviated to DS) [Japanese Published Unexamined Patent Application No. 51980/1987 (European Publication No. 183175)] (said genes being hereinafter referred to as AS gene, PRT gene, PRAI gene, InGPS gene, TS gene and DS gene respectively, in some cases), and strains carrying a recombinant DNA that contains PRAI-InGPS gene (Japanese Published Unexamined Patent Application No. 79775/1987).
With the increasing demand for L-tryptophan in recent years, improvement in the process for producing this amino acid has been desired. As a result of intensive studies to construct a new strain with higher L-tryptophan productivity by recombinant DNA technology, it has been found that L-tryptophan productivity can be increased by introducing into a strain belonging to the genus Corynebacterium or Brevibacterium a recombinant DNA containing DNA fragments bearing all of genetic information relating to the synthesis of DS, AS, PRT, PRAI, InGPS and TS, and the present invention has been accomplished. As stated above, L-tryptophan-producing strains carrying a recombinant plasmid DNA that contains genes relating to the biosynthesis of L-tryptophan, i.e. AS, PRT, PRAI, InGPS and TS genes (Japanese Published Unexamined Patent Application Nos. 156292/1984, 149082/1986 and 79775/1987), and those carrying a recombinant plasmid DNA that contains DS gene (Japanese Published Unexamined Patent Application No. 51980/1987) have been known. However, no example has been known which employs a recombinant DNA containing all of DS, AS, PRT, PRAI, InGPS and TS genes. The fact that L-tryptophan productivity can be further increased by simultaneous amplification of all of these genes has been first disclosed in the present invention.